3 rd Nine Week Benchmark Study Guide

1. 3rd Nine Week Benchmark Study Guide

2. 1. Define speed, velocity and distance in your own words. • Speed is the rate at which an object moves or how fast it is changing position. The unit of speed is distance/time like m/s or mph. • Velocity is both how fast something is moving and in what direction. • Distance is a change in an object’s position measured in meters in the metric system.

3. 2. Calculate speed. • Speed is calculated by dividing distance by time. • There is average speed which is the speed you calculate when speed varies. It is total distance / total time. • There is constant speed which is speed that doesn’t change. Again, this is calculated by dividing distance traveled by the time it took to travel that distance.

4. Example calculation: 1. A school bus driver begins his route at 6:30 a.m. with an odometer reading of 67,930 miles. He finishes his morning run at 9:30 a.m. and his odometer then reads 68,005 miles. What is the average speed of the school bus? Remember average speed = total distance total time Average speed = 68005 – 67930 = 75 miles = 25 mph 3 hrs 3 hrs

5. Example Calculation: • A car is traveling at a constant speed. After it has traveled 30 minutes, it has gone a distance of 60 km. What is its speed in km/hour? Speed = distance / time Time needs to be in hours 30 minutes = 0.5 hours Speed = 60 km / 0.5 hrs = 120 km / hr (about 70 mph)

6. 3. Explain how speed, velocity and acceleration are all unit rates A ‘unit rate’ is a how fast something changes in a unit of time (say 1 second or 1 hour). The denominator becomes 1 (a unit) when you divide. Speed = distance / time Velocity = distance / time in a given direction Acceleration = final velocity – initial velocity time

7. 4. Explain the difference between velocity and speed • Speed only tells how fast something is changing position • Velocity tells both how fast something is changing position and in which direction the object is moving

8. 5. Why do scientists find it necessary to have a different expression for speed and velocity? • Scientists often deal with objects that are changing direction (so velocity is needed) or several objects moving in relation to each other (so direction or velocity is needed). Stating DIRECTION in addition to SPEED completes the motion picture!

9. Be able to recognize on a graphs changing and constant speeds (note that these have the same average speed) No change in distance so speed is zero Constant speed; slope is the same distance distance Speed increasing; steeper slope Speed decreasing; slope is ‘flatter’ time time

10. 7. Define acceleration and name 5 different ways that an object can accelerate. • Acceleration shows how fast an object’s speed is changing. An object can accelerate by: • Speeding up • Slowing down • Changing direction • Speeding up and changing direction • Slowing down and changing direction

11. 8. Calculate acceleration Acceleration = final velocity – initial velocity time A car pulls off of I-85 South to an exit ramp slowing to a speed of 40 mph from a speed of 70 mph. It takes the car 1minute to slow down. What is the rate of acceleration? Acceleration = 40 – 70 mph = – 30 mph = – 0.50 mph 60 sec 60 sec sec The value is negative because the car is slowing down. Note: units are distance/time/time

12. Explain why we must know velocity rather than speed in order to determine acceleration. • Because acceleration can be defined as a change in speed AND/OR direction, an object moving at a constant speed is defined as accelerating if it is changing direction. • For example, a car making a turn moving at a constant speed of 25 mph is considered to be accelerating.

13. 10. Explain the differences of acceleration and velocity. • Velocity tells you how fast an object is moving and the direction in which it is moving. • Acceleration tells how fast an object’s velocity is changing… speeding up, slowing down and/or changing directions.

14. 11. Explain why an object traveling in a circle is constantly accelerating even if its speed/numeric value for velocity is constant. • The blades of this windmill are constantly changing direction as they turn at a constant speed. This centripetal force is an example of acceleration.

15. 12. Define and describe the difference between balanced and unbalanced forces. • You must have more than one force to have balanced or unbalanced forces. • Balanced forces combine for a net force of zero and result in no change in motion when applied to an object at rest or no change in motion when applied to an object moving at a constant speed and in a straight line. In other words, balanced forces don’t cause acceleration. • Unbalanced forces combine for some positive or negative net force. Unbalanced forces cause a change in motion.

16. 12a, b. Explain and draw force diagrams including both balanced and unbalanced forces and how these forces affect motion. Balanced forces result in no change in an object’s motion. The net force (after adding forces) is zero. FRICTION OPPOSING MOTION WHEELS PUSHING ON GROUND Net Force = 0 resulting in constant speed (no acceleration)

17. 12a, b. Explain and draw force diagrams including both balanced and unbalanced forces and how these forces affect motion. • Unbalanced forces result in a change in an object’s motion causing the object to accelerate (speed up, slow down or change direction). The net force (after adding forces) is either positive or negative. Net force = 75 + (- 50) = 25 N + 75 N - 50 N FRICTION OPPOSING MOTION WHEELS PUSHING ON GROUND Net force is positive resulting in positive acceleration Δ car speeds up.

18. 12c. Explain why we need to know a net force to determine an object’s motion. • Balanced forces have a NET FORCE of ZERO resulting in NO CHANGE in an object’s motion. • Unbalanced forces have a POSITIVE or NEGATIVE NET FORCE resulting in a CHANGE in an object’s motion.

19. 12d. Be able to identify the direction of motion based on the net force. An object will move in the direction of the net force if the net force is not zero. Net force is – 55 N Friction 20 N Pushing with a force of - 75 N Pushing with a force of - 75 N Net force is – 55 N Friction 20 N

20. 12d. Be able to identify the direction of motion based on the net force. An object will move in the direction of the net force if the net force is not zero. He pulls up against the pull down of gravity. The magnitude of the forces is equal to the weight of the boxes with an equal force. The net force is zero, so the boxes do not fall or move up.

21. 12d. Be able to identify the direction of motion based on the net force. An object will move in the direction of the net force if the net force is not zero. + 40 N + 40 N - 10 N Net force + 30 N The net force is + 30 N to the right (+ direction). Because the net force is not zero, this pair of forces is unbalanced resulting in motion of the grocery cart. - 10 N

22. 13. What is the abbreviation for and unit name for force in the international system of measurement? The unit of measure for force is the Newton, abbreviated N. He’s lifting barbells with a weight of 5 N! 5 5

23. 14. Newton’s Laws: Explain each in your own words Newton’s First Law has to do with inertia which is related to an object’s mass. The more mass or inertia an object has, the harder it is to get it to move OR the harder it is to change its movement. Also, objects that aren’t moving or that are moving at a constant speed and in a straight line will keep doing what they’re doing unless an unbalanced force causes the motion to change. The baseball has low inertia (mass) and we can make it move with minimal force. It will just sit here unless an unbalanced force is applied.

24. 14. Newton’s Laws: Explain each in your own words Newton’s Second Law tells us how force, mass and acceleration are related. Basically, if you want something to move, that something has a mass (m). To get it to move, you have to apply a force (F). The equation F = ma will tell you the rate of acceleration (a). If the dude wants to make the ball speed up a lot (high rate of acceleration), he is going to have to apply a big kick (force) to it.

25. 14. Newton’s Laws: Explain each in your own words Newton’s Third Law tells us that forces come in pairs. When a force acts on an object, that object exerts an equal and opposite force back on the first object. Example: When you walk down the street, you push off of the street and the street pushes back on you.

26. 15. Calculate acceleration given a force and a mass. How fast will a baseball accelerate if it has a mass of 0.145 kg and is hit with a force of 3400 N? F = ma solving for a gives us a = F/m a = 3400 N / 0.145 kg a = 23,400 m/s/s

27. 16. Understand the relationship between force, mass and acceleration Newton’s Second Law tells us how force, mass and acceleration are related. For constant mass: F = ma as F↑ a↑ and as F↓ a↓ For constant Force: F = ma as m↑ a↓ and as m↓ a↑ For constant acceleration: F = ma as F↑ m↑ and as F↓ m↓

28. 17. Define and explain the properties of inertia Inertia is basically an object’s tendency to resist a change in its current state of motion. Inertia is proportional to mass. An object that has low inertia (mass) will be easy to move if it is not moving. An object that has high inertia (mass) will be hard to move if it is not moving The same is true of changing the object’s motion if it is moving…

29. 18a and 18b: Give examples of objects with greater inertia and explain why it’s harder to make this object accelerate. The more mass something has, the more inertia it has. It’s hard to make this object accelerate (speed up, slow down and/or change direction) because it has a lot of MASS to move differently.

30. 19. How do we measure weight and inertia? • Weight is measured with a scale that shows how much gravity is pulling on an object. • Inertia is measured indirectly by determining how much force has to be applied to make something accelerate.

31. 20. Friction • Friction is a force that opposes motion. Friction is due to contact of surface and the force between them. • There are several types: sliding, rolling, fluid (including air resistance) and static (between two surface that are not moving).

32. 21. Explain what happens in terms of Newton’s Laws to an object with balanced forces when friction is added. Because friction is a FORCE that acts in the opposite direction of an applied force, friction will SLOW an object that is moving at a constant speed. Static friction is also responsible for a small part of an object’s inertia (its tendency to NOT move)

33. 22. Be able to identify the direction of frictional force in an illustration when the direction of motion is identified. Friction OPPOSES motion so the friction force arrow will be in the opposite direction of motion. MOTION friction friction

34. 23. What are some ways to reduce friction? You can reduce friction by: • Minimizing force between objects • Making surfaces more regular or smooth • Use wheels or change sliding to rolling friction • Use a fluid as a lubricant – water, oil, grease

35. 24 and 25. Define gravity and state the Law of Universal Gravity Gravity is a pulling force exerted by anything that has mass. The Law of Universal Gravity says that: ALL objects attract each other with a force of gravitational attraction. Gravity is universal.

36. 26 and 27. Where does gravity exist and what affects it? Gravity exists everywhere. Gravity is affected by an object’s mass and it’s proximity (closeness) to other objects. Gravity increases as an object’s mass goes up (and goes down as mass goes down). Gravity increases as objects get closer together (and decreases as they get farther apart).

37. 28. Be able to explain the relationship between mass and weight. MASS is how much stuff is in something. WEIGHT is a measure of how gravity pulls on something’s mass. MASS will not change. WEIGHT changes depending on the source of gravity.

38. 29. Be able to find both the acceleration, speed and distance an object will reach when dropped. Remember that the pull of gravity (acceleration) here on Earth is g = 9.8 m/s/s. This is a CONSTANT and does not change (for the most part). To find an object’s speed after a certain number of seconds, multiply 9.8 m/s/s by the number of seconds. v = gt where g = 9.8 m/s/s and t is time To find the distance traveled, use the formula h = 1/2 g t² where g = 9.8 m/s/s and t is the time in seconds

39. 30. Explain how satellites and orbits work. • Satellites are able to remain in an orbital motion because of a balance between gravity pulling on an object (free fall) and its forward motion at a constant speed. When these are in balance, the satellite maintains its orbital motion. • This force is called centripetal force.

40. 31. Identify the force of gravity that would produce the greater or lesser acceleration. Gravity from a less massive object will produce less acceleration. Gravity from a more massive object will produce more acceleration. Gravity from objects farther from each other will produce less acceleration. Gravity from objects that are closer together will produce more acceleration.

41. 32 and 33. Why can zero gravity never exist and why can an object never truly be weightless? Gravity exists everywhere. An object can never truly be weightless because gravity, that is everywhere, gives an object weight due to the force pulling on its mass.

42. 34 and 35. • What are some tools/instruments used to measure mass and/or weight? • Mass- balance • Weight- scales • What is the relationship of mass and weight with regards to the force of gravity? Mass- stays the same regardless of gravity Weight- depends on gravitational force

43. 36a. Define work and explain how you can determine if work is done on an object Work (scientifically) is done on an object when a force is applied and results in the object moving in the SAME direction as the applied force. Example: When you write with a pencil, you are doing work on the pencil because the pencil moves in the direction in which you push.

44. 37. Practice calculating work and know the unit of measure. Work = Force X Distance (in same direction) Newtons X meters = N ● m = joule If you push a box with a force of 30 N and the box moves 4 meters, how much work have you done on the box? Work = F ● d = (30 N)(4 m) = 120 joules (j)

45. 38 and 39. Define power and practice calculating it. What is its unit of measure? Power is the RATE at which work is being done. Power = work Example: How much power time does a machine have that can do 500 j of work in 50 seconds? Power = 500 j / 50 sec = 10 watts

46. 40. Explain how energy is conserved using a simple machine. Because energy cannot be created or destroyed (law of conservation of energy) using a machine does not enable us to get more energy out than we put in. A machine only makes the work easier to do by changing the size of the force required or the direction of the force. If the size of the force changes, the distance the object moves must change too. Remember: Work in = Work out Most of the time it is Work in = Work out + heat

47. 41. Explain how changing the output force affects the distance and the amount of work done. (see page 195) The output force is the force that results from using a machine. The input force is the force put into the machine. Because the equation for work is W = F x d decreasing the output force will increase the distance and increasing the output force will decrease the distance. This is the force/distance trade-off.

48. 41a and b. Explain how work input and work output are different but related. How do machines make work easier? Because work is constant, the amount of work we put in is equal to the amount we get out. HOW that work gets done (force x distance) is how they differ. Because machines only make doing the work EASIER, machines do not change the AMOUNT of work done. The goal of machines is to make the forces and distances change to make the work easier.

49. 42. Explain how work changes if the force or distance is changed. Because the equation for work is: Work = Force x distance as F ↑ d ↓ (work stays same) as F ↓ d ↑ (work stays same) If the force stays the same (magnitude) and only the direction changes, the distance will be the same.

50. 43. Explain how the six types of simple machines operate and give an example of each. See Section 8.3 for this. Make sure you look at the diagrams to understand how each works and the differences between the three types of levers.